Download or read book The Development of an Improved Thermionic Energy Converter written by and published by . This book was released on 1965 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Development of an Improved Thermionic Energy Converter written by and published by . This book was released on 1965-04 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Development of an Improved Thermionic Energy Converter written by Radio Corporation of America. Direct Energy Conversion Department and published by . This book was released on 1965 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Development of a Low work function Collector for Thermionic Energy Converters written by P. K. Shefsiek and published by . This book was released on 1965 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report covers the full year's work toward the improvement of thermionic energy conversion. This work can be divided into two separate tasks which were concerned respectively with the analysis of special materials to enhance low work function in collector electrodes and the development of a mathematical equation to describe converter performance in terms of physical parameters and conditions. The analysis of materials verified prior work that matrix surfaces delivered improved performance over other electrode surfaces. Of the materials evaluated during the report period, tantalum was superior to tungsten, molybdenum and iridium while nickel was inferior to the three median matrices. The mathematical equation relates output potential to the other parameters of current density, emitter temperature, collector temperature, cesium temperature and electrode spacing. The functional relationships of the converter parameters used in the equations are based on the general theoretical model of thermionic converter operation. The coefficients assigned to each term of the equation are determined by application of linear regression statistical analysis to measured voltage current data. The analysis has been applied to data from several different electrode pairs from different laboratories with excellent correlation with measured data over a wide variation in parameters. (Author).
Download or read book The Development of a Thermionic Converter Module Suitable for Liquid Metal Heating written by G. Y. Eastman and published by . This book was released on 1964 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Effort was continued to improve performance and increase the reliability of thermionic energy converters for space applications. The particular objectives include optimization of geometry and ceramic insulation between emitters and heat source. This work will include the development of a thermionic generator module to develop 3.0 volts of potential from a liquid metal heat source. The overall concept of the 3-volt generator has been established. Before final design and fabrication of the generator, the more difficult problems are being solved by fabricating and testing prototype 3-converter modules. During this period, four 3-converter modules were assembled. A number of subassemblies were successfully tested and techniques for assembling a series of converters within a single envelope were perfected. A method of bonding the center heat source tubing has been tentatively selected and materials for detailed evaluation of the method have been ordered. Life testing of one Type A1198B converter was concluded after 1010 hours. Another converter of this type has since completed 600 hours of a life test with a constant output of 46 watts. (Author).
Download or read book Application of Semiconductors to Thermionic Energy Converters written by Daniel C. Riley and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy conversion (TEC) is a direct heat-to-electricity conversion technology with the potential to leapfrog state-of-the-art solid-state conversion in efficiency and power density. In a thermionic energy converter, electrons evaporate from a hot electrode, the cathode, into a vacuum gap and are collected by a cooler electrode, the anode, to generate electric current. In the 1960s-1970s numerous groups reported thermionic converters with power densities above 10 W/cm^2 and conversion efficiencies of ~15%. However most of this work was tied to the US space-nuclear program which ended in 1973, and thermionics research has never fully recovered. As a result two central challenges yet remain in thermionics: (1) High operating temperatures necessary to produce electric current result in difficult materials challenges, and (2) low operating voltages due to losses associated with space charge and high anode work functions. However, new opportunities to tackle these challenges are available as a result of the breathtaking rise of semiconductor fabrication technology. In this work I present a new physical mechanism called photon enhanced thermionic emission (PETE). This concept is an improvement on thermionic emission by using light to boost the average energy of carriers in a hot p-type semiconductor cathode. Additionally, unlike in a photovoltaic cell, the waste heat from recombination losses and sub-bandgap light absorption is utilized to heat the cathode. Thus a PETE cathode can produce efficient electron emission at lower temperatures than a thermionic cathode. I will describe theoretical calculations showing that a PETE device may exceed 40% solar power conversion efficiency, and the conversion efficiency may exceed 50% if a PETE device is used in tandem with a solar thermal backing cycle. I will also describe an experimental demonstration of the PETE effect in an ultra-high vacuum photoemission measurement. In the cathode of an energy converter based on photon-enhanced thermionic emission (PETE) photoexcited carriers may need to encounter the emissive surface numerous times before having sufficient thermal energy to escape into vacuum and therefore should be confined close to the surface. However, in a traditional planar geometry, a thin cathode results in incomplete light absorption. Nanostructuring has the potential to increase light capture and boost emission by decoupling the lengths associated with photon absorption and electron emission. Nanostructures may complicate the properties of the emissive surface; therefore, the effect of nanostructuring on emission efficiency needs to be studied. In this work I describe results from a suite of simulation tools we have developed to capture the full photoemission process: photon absorption, carrier transport within the active material, and electron ballistics following emission. I show that the theoretical efficiency of a negative electron affinity emitter may be increased with nanostructures if light absorption and electron escape ballistics are considered. I then describe measurements of the photoemission efficiency of fabricated nanostructures that were designed based on the results of the simulation suite. I will also present a fundamentally new method to increase the operating voltage of a TEC by lowering the anode work function using the surface photovoltage effect. When a semiconductor surface is illuminated, photo-excited carriers form an internal dipole, or surface photovoltage (SPV), in the band-bending region and begin to flatten the bands near the surface. This SPV is analogous to the photovoltage in a photovoltaic cell and can reduce the effective work function of the material. I will describe an experimental demonstration using the SPV effect to produce a low work function surface. I will also describe a proof-of-concept demonstration of the SPV effect applied to improve the I-V characteristics of thermionic device. This generic physical process extends across materials systems and forms a realistic path to ultra-low work functions in devices to enable efficient thermionic energy conversion.
Download or read book Thermionic Energy Conversion written by George N. Hatsopoulos and published by . This book was released on 1979-01 with total page 683 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prepared under the auspices of the U.S. Department of Energy Division of Power Systems. Volume I of Thermionic Energy Conversiondealt with processes and devices (MIT Press, 1974). Its four chapters summarized information basic to the field and not subject to substantial alteration by future developments. Volume II begins with chapter 5 and describes the scientific and engineering aspects of thermionic conversion and the experience with actual operational hardware. It summarizes the experience and analytic methods that should be useful in the development of new applications of thermionic conversion. Thermionic Energy Conversionis intended for scientists and engineers working in the field of energy conversion. With increased interest in maximizing the efficiency of present energy conversion systems, it is an important reference for scientific and engineering libraries as well. The book benefits especially from the authors' actual experience-Hatsopoulos and his firm, Thermo Electron Corporation, are leaders in this field. Gyftopoulos and his students have made basic contributions to the theory of thermionic conversion. Both authors have developed a unified quantum theory of mechanics and thermodynamics. The book covers Elements of Quantum Mechanics; Principles of Thermodynamics; Thermodynamics of Stable Equilibrium States; Thermodynamics of Steady States; Emission Phenomena; Collisionless Transport Phenomena; Analysis of Performance Characteristics of High-Pressure Diodes; Experimental Techniques; Experimental Studies and Correlations of Characteristics; Metallurgy of Electrode Materials; Design and Fabrication of Practical Convertors; and Thermionic Power System Engineering.
Download or read book Thermionic Energy Converter written by Dr. Walter L. Knecht and published by . This book was released on 1960 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research Studies on Thermionic Converters Emitter Shell Phase Report Number 5 written by G. Y. Eastman and published by . This book was released on 1965 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Microfabricated Thermionic Energy Converters written by Jae Hyung Lee and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy converters (TECs) are heat engines that convert heat directly to electricity at very high temperatures. This energy conversion process is based on thermionic emission--the evaporation of electrons from conductors at high temperatures. In its simplest form, the converter consists of two electrodes in the parallel plate capacitor geometry, and it uses the thermionically emitted current to drive an electrical load. This dissertation presents research on five key areas of microfabricated thermionic energy converters ([mu]-TECs). First, the numerical calculation of the emitter-collector gap that maximizes the power conversion efficiency of thermionic energy converters (TECs) is discussed. Thermionic energy converters require emitter and collector work-functions that are relatively low, to reach useful efficiencies at typical operating temperatures of 1000 - 1500 oC. The optimum arises because efficiency drops both at very large gaps, due to space-charge limitations on the TEC current, and at very small gaps, due to the increased heat loss via near-field radiative heat transfer. The numerical calculation results show that, for typical TECs made with cesiated tungsten electrodes, the optimal gaps range from 900 nm to 3 [micrometers]. I then discuss several prototypes of mechanically and thermally robust [mu]-TECs, including the stress-relieved emitter design, emitter-collector structural design, as well as a recent approach for the stand-alone (encapsulated) [mu]-TECs. Thermionic emission from the SiC emitter was demonstrated for the first time. The stress-relieved design emitters were analyzed, and the work-function of the SiC emitter was estimated at temperatures of up to 2900K. Also described are both the planar and the U-shaped suspension for microfabricated TECs ([mu]-TECs). Our initial planar [mu]-TECs achieved emitter temperatures of over 2000 K with incident optical intensity of approximately 1 W/mm2 (equivalent to 1000 Suns), remained structurally stable under thermal cycling, and maintained a temperature difference between the emitter and the collector of over 1000 K. Conformal sidewall deposition of poly-SiC on a sacrificial mold is used to fabricate stiff suspension legs with U-shaped cross sections, which increases the out-of-plane rigidity and prevents contact with the substrate during the heating of the suspended emitter. By extending the conventional technique of cesium coatings to SiC, we reduce the work-function from 4 eV to 1.65 eV at room temperature. Subsequently, we tested [mu]-TECs with both barium and barium oxide coatings. The coatings reduced the work-function of the SiC emitter to as low as ~2.14 eV and increased the thermionic current by 5-6 orders of magnitude, which is a key step toward realizing a efficient thermionic energy converter. Encapsulation of [mu]-TEC was achieved by an anodic bond between pyrex and the silicon substrate with via feedthroughs. Last, I introduce the photon-enhanced thermionic emission (PETE) concept, and show why a single crystal photo-emitter is needed. I cover my recent fabrication development of smart-cut layer transfer using Spin-on-Glass (SoG). In addition, a novel layer transfer technology that can transfer any device materials onto the glass substrate, which I call "Anything on Glass, " is briefly described. I, then, describe how the first demonstration of the photon-enhanced thermionic emission (PETE) from the microfabricated emitter was achieved. The p-type SiC emitter was used to demonstrate PETE in an uncesiated and microfabricated sample, bringing this energy conversion approach closer to practical applications.
Download or read book Design and Development of a Test Device for Optimizing Thermionic Energy Converter Efficiency written by Robert Leo Bailey and published by . This book was released on 1962 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Low Work Function Material Development for the Microminiature Thermionic Converter written by Donald Bryan King and published by . This book was released on 2004 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy conversion in a miniature format shows potential as a viable, high efficiency, micro to macro-scale power source. A microminiature thermionic converter (MTC) with inter-electrode spacings on the order of microns has been prototyped and evaluated at Sandia. The remaining enabling technology is the development of low work function materials and processes that can be integrated into these converters to increase power production at modest temperatures (800 - 1300 K). The electrode materials are not well understood and the electrode thermionic properties are highly sensitive to manufacturing processes. Advanced theoretical, modeling, and fabrication capabilities are required to achieve optimum performance for MTC diodes. This report describes the modeling and fabrication efforts performed to develop micro dispenser cathodes for use in the MTC.
Download or read book Renewable Technologies written by Mohammad Islam and published by LAP Lambert Academic Publishing. This book was released on 2010-06 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermionic energy converter (TEC) is a device to generate electricity from heat in a silent, vibration-free operation. Non-idealities such as negative space-charge effect and electron reflection from collector surface adversely effect output current density and device efficiency. Using a range of thin film deposition techniques such as rf plasma magnetron sputtering, electrochemical deposition and electroless process, different surface structures were developed and tested for suppression of electron reflection using Cs/O vapor plasma TECs. Principles of both vacuum and solution based synthesis of thin films, and promising device configurations for thermionic energy converters are presented. This book overviews evolution of thermionics technology in a comprehensive manner, identifies key issues and challenges to be addressed, and suggests feasible solutions based on a sensible choice of materials and processes. The contents of this book are useful for teaching at both undergraduate and postgraduate levels as well as for researchers working on thin film synthesis and characterization for applications in energy, microelectronics, and surface engineering industries.
Download or read book Energy a Continuing Bibliography with Indexes written by and published by . This book was released on 1975 with total page 610 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ERDA Energy Research Abstracts written by United States. Energy Research and Development Administration and published by . This book was released on with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ERDA Energy Research Abstracts written by United States. Energy Research and Development Administration. Technical Information Center and published by . This book was released on 1976 with total page 588 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Government wide Index to Federal Research Development Reports written by and published by . This book was released on 1966-02 with total page 1050 pages. Available in PDF, EPUB and Kindle. Book excerpt:
